This invention relates generally to golf clubs and, in particular, to golf club shafts.
Typically, golf clubs include an elongated shaft, a club head attached to the lower end of the shaft, and a grip attached to the upper end of the shaft. It is well known that when a golf club is used to strike the golf ball, the impact between the golf club head and the golf ball causes the golf club shaft to vibrate. When a golfer swings a golf club so that the club head impacts the golf ball at the club head""s center of gravity, generally, no unpleasant vibrations are experienced. However, if the club head impacts the golf ball at a location that is offset from the center of gravity, unpleasant vibrations are transmitted through the club head, the shaft and the grip to the golfer""s hands. Various methods have been proposed to damp the unpleasant vibrations resulting from such a mis-hit.
U.S. Pat. No. 5,294,119 to Vincente, et al. discloses a vibration damping device for golf clubs that is located on the shaft adjacent the club head or the grip. In one embodiment, the damping device consists of an outer ring made of a rigid material such as metal and an intermediate layer made of a visco-elastic material. The intermediate layer has an inner surface bonded to the outside of the shaft and an outer surface bonded to the inside of the outer ring. In another embodiment, the damping device consists of a rigid cylindrical ring disposed within the hollow golf club shaft. A visco-elastic intermediate layer has its outer surface bonded to the inner surface of the golf club shaft and an inner surface bonded to the outer surface of the rigid ring.
U.S. Pat. No. 5,655,975 to Nashif discloses a vibration damping device consisting of a flexible rod disposed within and extending substantially the entire length of the golf club shaft. The rod is bonded to the inside surface of the golf club shaft by a visco-elastic material interposed between the shaft and the rod. According to the patent, the rod is flexible and has resonant frequencies over the same frequency range as the shaft such that the shaft and rod vibrate out of phase with respect to each other and thereby deform the visco-elastic material thereby damping vibrations in the shaft.
U.S. Pat. No. 5,683,308 to Monette discloses a vibration damping device consisting of a solid shaft disposed inside the golf club shaft extending substantially the entire length of the shaft. The rod is secured to the interior surface of the golf club shaft by means of plural resilient and non-resilient discs interposed between the rod and the interior surface of the golf club shaft. Although these and other vibration damping apparatus mitigate with varying success unpleasant vibrations transmitted by the golf club shaft, they do so only at the expense of energy lost in the form of frictional heat generated in the visco-elastic material, and do not address the basic biomechanical interaction between the mode shapes of the golf club shaft and the human golfer.
U.S. Pat. No. 5,297,791 to Negishi discloses a golf club shaft having a single vibration preventing piece composed of a shape memory alloy clamped to the shaft at a location generally coincident with the kick point (i.e. the antinode of the second mode) of the shaft.
U.S. Pat. No. 5,703,294 to McConnell, et al. addresses the need to evaluate the vibration characteristics of golf clubs with the purpose of improving the feel by selecting a golf club head and shaft combination that produces node lines that intersect to form a triangular region proximal the center of the face of the club. McConnell fails to recognize, however, that a major contributing factor to the feel of a golf club is the modal shape proximal the golf club grip, where the interface between the shaft and golfer occurs.
What is needed is a golf club in which the vibration characteristics of the shaft are tuned to produce nodes of the dominant flexural bending modes proximal both the face of the club and the grip.
The present invention solves the foregoing need by providing a method of measuring the flexural vibration mode frequencies of a golf club for the purpose of determining optimum placement of a plurality of discrete shaft stiffeners. A golf club constructed in accordance with the principles of the present invention comprises a shaft, a golf club head, a grip and a plurality of discrete shaft stiffeners. The shaft stiffeners are strategically located along the shaft so as to shift the nodes of at least the second and third flexural vibration modes such that a node of each of the second and third flexural vibration modes occurs both at the club face and proximal the golf club grip. Preferably, the stiffeners are located so as to shift the nodes of the second through fifth flexural vibration modes such that a node of each of the second through fifth vibration modes occurs both at the club face and proximal the golf club grip. By suppressing certain vibration modes to cause node lines at both the club face and grip, both accuracy and comfort are increased.